Intestinal bacterial, fungal, and methanogen overgrowth

Small intestinal bacterial overgrowth (SIBO), intestinal methanogen overgrowth (IMO), and small intestinal fungal overgrowth (SIFO) are defined by the presence of abnormal and excessive bacteria or methanogens or fungal elements in the small bowel, and intestinal methanogen overgrowth (IMO) by the presence of excess methanogenic archaeas in the gastrointestinal (GI) tract. As methanogens are classified under the kingdom of archaea and are not bacteria, the proper term for excess methane-producing microbes in the gut is IMO. These three overgrowth entities have been associated with a constellation of gastrointestinal (GI) and systemic symptoms such as diarrhea, constipation, alternating bowel habits, bloating, flatulence, eructation, abdominal discomfort, nausea, dyspepsia, and fatigue, and brain fog. Classically described serious manifestations of overgrowth such as malabsorption, severe weight loss, anemia, and deficiency of vitamins and iron are less frequently seen in modern days. Its their exact prevalence is unclear because these problems require diagnostic tests, but they haves been estimated to affect at least 33% of patients with unexplained GI symptoms or those with irritable bowel syndrome.